Hi, it's been a while since I played around with the Dish 500 on 61.5 and 72.7 but the best I can remember is after you split the signals between the two satellites you should come up to about 5 points less on each satellite over what you could get by fully peaking on just one. The signal quality will be down a little but still more then enough to get a solid lock. You would see more rain fade with this setup but it will work most of the time just fine. On another note you could peak more on one satellite then the other if more of the channels you want are on that satellite - for example, peak on 61.5 and take whatever you get on 72.7 that would give you maximum signal on the most watched channels. This would give you less rain fade on the channels you want the most.
Hope this helps, DC