I don't think the weight of the racket is what's making you tired. Its more likely your fitness, or the racket set up is low powered and you are swinging quite hard and tiring out. Here is a recent thread on fitness, my post is on the second page #25: http://tt.tennis-warehouse.com/showthread.php?t=440007
Some running and sprinting even 1x or 2x a week can go a long way, if you don't already do that.
I'm not sure how you feel about the Swingweight of your frame, but it seems pretty good in stock form. You can try a lighter replacement grip to reduce the overall weight of the frame, like a Babolat Skin Feel grip - compared to most stock grips, it makes a frame feel noticeably lighter. What string & tension are you using? You can use a more powerful string set up for more pop.
Otherwise, most of the tweeners are good choices. The Pro Open is a good starting point, the current BLX Blade has the same string pattern and similar SW as your frame but is lighter and is supposed to have good power.