If you can find the gun with the power you want then thats the way to go. Changing a spring would be dangerous without a spring compressor, which you would probably have to make yourself although there are plenty of examples on the internet. Slavias are known for there solid construction rather than their power, Dianas can be very powerful and are pretty well made but incorporate a little more plastic, HWs are usually better built yet but the price goes up as well. Crosmans, Benjamins and Daisys are hit and miss but there are good models of those, particularily the nitro piston models. The most important thing to remember is not to shop at Canadian Tire, even when they are on sale you will be able to find a better deal from an online dealer, unless your local gun shop can get what you want. One last thing, high power and .177 are not the best combination even with the heaviest pellets, .22 will give better all round performance especially if you were planning to hunt with it.