A R34 GTT SMIC will support just over 200 kW's
280 Bhp = 208.80 kW's (Approx)
Anything above that I would go OEM GTR FMIC as they are good for over 300 kW's (402.31 Bhp, approx)
A OEM GTR FMIC would be cheaper then a Blitz one and you would gain a similar result until you want more power.
LOL! I measure power in kW's not Bhp, so I have to do some conversions.
Installing a FMIC will allow better flow, more cooling surface, which in result you may gain a slight boost increase, but I don't see it boosting from 255 Bhp to 280 Bhp.
+ You have the stock turbo from a R33 GTS-T, I would not go anything higher then what your doing, unless you have rebuilt the stock turbo with steel internals, the ceramic internals will not last long.