Since you have mentioned you want a powerful motorcycle, we would recommend you look at the Triumph Scrambler 400X, KTM 250 Adventure and TVS Apache RTX 300 in the ADV / Scrambler category. Of the three, the Triumph bike is the most powerful, but it is also pleasantly usable inside the city, whereas the KTM and TVS are more do-it-all machines that will also be wonderful on a day-to-day basis. 

Coming to the Xpulse 421, there's no official communication from Hero on when it will be launched, so we would recommend going with any of the other options you are considering. 

Take a test ride of whichever option you shortlist before you choose. 

Since you have had a good experience with a Honda machine, you could stick with the brand and go with the Honda CB300F. The CB300F is light, comfortable, spacious and will return decent fuel economy. If you want to switch brands, the Bajaj Pulsar N250 and the Suzuki Gixxer 250 make for good upgrade options with their smooth engines and comfortable ergonomics. 

If you don't mind staying in the same displacement range while getting a significant performance bump, the KTM 160 Duke and Yamaha MT-15 warrant consideration. With their liquid-cooled engines and light weights, these two will give you the performance step up you want without sacrificing on mileage. 

If you are comfortable with the size and heft of the TVS Apache RTX 300, then it is certainly worth considering because it will fit your needs quite well. 

If you want something in the same price range that is lighter and more manageable, then bikes like the Bajaj Pulsar NS400Z and the KTM 250 Duke are worth considering. 

Take exhaustive test rides of all the machines you shortlist before you decide. 

A new bike will come with a warranty, and you will be the first one to break it in, so the peace of mind of buying a new machine is not to be discounted. 

If you are looking at older bikes that are 4-5 years old or more, then you will also need to budget for a comprehensive service and perhaps some replacement cycle parts like tyres and brakes. 

While the KTM 390 Duke is a great option, you could also look at the Royal Enfield Guerrilla 450 since you've already owned a bike from the same brand. 

Stepping up from 20hp to 130hp in a single shot doesn't seem like the safest upgrade. We would like to recommend that you upgrade to something more approachable, like the KTM 390 Duke seems like a more sensible option. If you still want a multi-cylinder bike, something like the Kawasaki 650 and the Honda 650, as well as the CB750 Hornet will be more manageable. 

Try and take a test ride of everything you're considering before you put your money down. 

Some options you can consider are the TVS Apache RTR 310, KTM 390 Duke, Triumph Speed 400 and Royal Enfield Guerrilla 450. The Triumph and Royal Enfield aren't as overly sporty as the other two and will have a more effortless riding experience owing to their torque delivery, which is earlier in the rev band. 

The KTM 390 Duke is a proven product when it comes to sheer speed, but in its latest avatar has become quite compact, which may not be the best thing if you are a larger person. 

Last but not least, the TVS Apache RTR 310 has great handling and reasonable performance. We would recommend getting the variant with the quickshifter on the TVS as that offers the best value for your money. 

Take a test ride of everything you're considering before you decide. 

Since you are used to a good amount of performance, we'd suggest you move to something like the Triumph Speed 400. This bike will meet your needs of having a comfortable riding position as well as a reasonably low seat height. 

There are more comfortable options available, but almost all of them are adventure bikes with relatively tall seats. If you can get along with a taller seat, we'd recommend options like the Royal Enfield Himalayan 450 or KTM 390 Adventure as good replacements for your Aprilia RS 457. 

For your usage, in the cruiser space, you can take a look at the Royal Enfield Classic / Bullet 350 as well as any of the three Honda CB350 models. All bikes have relaxed, smooth engines, spacious seats and great suspension comfort. 

In the ADV space, options like the TVS Apache RTX 300 and KTM 250 Adventure can be considered for their punchy - but not overwhelming - performance, spacious seats and comfortable ride quality, as well as luggage carrying capability. 

Take thorough test rides of all shortlisted options before you decide.

The TVS Apache RTX 300 and KTM 250 Adventure will both fit the bill for your needs. Both have spacious seats, will return decent fuel economy, have great suspension and ride comfort and should be light on the pocket. Do bear in mind that these bikes are significantly more powerful than the Unicorn you currently have, and if you want something that's more laidback, there are other options. 

Bikes like the Royal Enfield Bullet / Classic 350 and the three Honda CB350 models will also fit the bill if you don't mind their laidback character and retro looks. 

We recommend a thorough test ride before you choose.