[GuyBFF]

T Fittings in themselves do present a restriction to flow, but with your big pump it shouldn't be that bad unless theres something directly blocking the flow of water in them.

51c under load isn't too high, but if you want to overclock any further it would definetely help to get it lower (especially so there's headroom to Vmod).

Is there any air left in the rad? Try turning your computer so it can rise out (don't allow air in the T-fitting/fill tube to get back in however).

It could help to reduce your voltage. Some people have found success at lower overclocks at 1.6-1.7 volts on TBirds! Once you do go for higher mhz or if this doesn't work you will need however to V+. Try 1.6 to 1.7 in BIOS (which will likely be 1.7 - 1.8 once running). Lower voltage will definetely lower temps, sometimes this outweighs the voltage being lower, other times it just needs the juice.