I think what will happen is down the road when my card becomes outdated i will SLI
and i will do some OC down the road also
A system with a single GTX 570 requires a 600W PSU with 40A on the 12V rails and two 6-pin PCIe power connectors. Two of them running in SLI mode requires a 850W PSU with at least 58A on the 12V rails and four 6-pin PCIe power connectors. These requirements are for factory, stock-clocked GTX 570s.
The TX750 has 62A on the 12V rails and four 6+2 pin PCIe power connectors. It is sufficient for a system running two GTX 570s in SLI mode. Because your GPUs are factory OCed I would do any further OCs to the GPUs in small increments and try to stay at stock Vcore for CPU OCs; small increments with stress-testing for stability on each incremental increase.
If you wait too long, then you may have an issue finding another GTX 570 for your SLI. Nvidia will start to phase out the 570s now that the 600 series GPUs are on the street. On the bright side, as Nvidia and retailers clear stock to make room for the new GPUs there will definitely be some good deals on these cards. Just be careful how long you wait...