heres my opinion on thr lt-r vs the yfz. In stock form! I have a yfz and my brother n law has a lt-r he's a little lighter then me about 50 lbs lighter he's 170, I'm 220. We are equally skilled riders. We raced several times and in stock form the yfz pulls by 1 to 2 bike lenghts.
Now my brother in law put a cherry bomb and yoshi rs-5 full exhaust with spark arrestor out and no air box lid vs my yfz without an air box lid with K&N with billet adapter without the screen in the air box, spark arrestor out of stock exhaust and rejetted. The yfz pulled until about the beginning to middle of 4th gear then the lt-r gained a lot of power up top. Probably 3-4 bike lenghts.
Next I was going to retard the exhaust cam on the yfz and thats suppose to give you more power up top with little bottom end scarafice.
Now with that said my brother n law has spent about 650 dollars between the exhaust and cherry bomb and I only spent about 125 dollars for some jets and k&n with billet adaptor. After I retard the cam If I beat him the only mod that I spent money on is the K&N the bike is still pretty much stock, imagine with an aftermarket exhaust probably acouple more HP's.
My opinion is both quads are good, I prefer the yfz because the power delivery feels strong all the way from bottom to top, the lt-r power delivery feels way to smooth for my comfort, I like to feel the power hit a little hard, thats probably because of my love for 2 strokes!!!! The lt-r sits a lttle too high for my comfort, but the lt-r has the better suspension feels softer and easier on the body for track or dunes. It's all going to come down to personal perferences and I hope this helps you in some way, if there is any other info you would like to know you can give me a shout and I'll help you to the best of my knowledge vs the 2
I have no idea with the kfx450 sorry!!