I have a 36 oz 25" sirupati, and for me it's often a one and a half hand blade. The 26 oz 20" sirupati is a one hander with a decent reach, good for limbing with enough oomph to chop thick stuff, but the greater weight and velocity of the 25" one makes a big difference to true chopping. But my 19" 22 oz chitlangi is thinner, slightly lighter, and aimed properly often outchops the 20" sirupati. And it's easier to aim the chitlangi and I prefer its balance. I guess I'd say to go for the sirupati if you want a longer, slender blade that seems more indestructable and costs less, too. A 21" chitlangi is on my wish-list, I think one will out-do the 20" sirupati by a decent margin.
My 15" AK is about equal or maybe better than the 20" sirupati for dedicated chopping of hard wood. The AK is easier to use if reach isn't an issue. I think the greater reach of of the 20" sirupati is the only advantage between the two, and I'd thus prefer the sirupati or chitlangi for limbing or felling smaller trees.
But my 19", 3lb GRS totally outclasses everything else for true chopping, and is about as much as I can handle one handed when I'm NOT tired, and working below waist height. It is often easier for me to control than the 25" sirupati. So I think a 18" AK is on my list too. I also have a 19" WWII style HI villager (seems slightly less belly than a WWII), and it seems to be a good, easy to handle all-rounder, but going by my 15" AK, an 18" AK would definately outchop it. But I think I'd prefer the WWII-like village model for working thinner stuff above wist height over the AK (I think a chitlangi would be better than either for that though)
It really seems like if the $ are available, going for the costlier models with the fullers is well worth it.
Sizewise, I'm 5' 10', 165 lb, and in slightly better than couch-potatoe shape (used to weigh 130). Hope this helps you decide.