Compared to doing nothing climbing is the better option is it not? Its not the absolute ceiling so there will be some room left to manoeuvre within and maybe 10 - 20 knots of speed to trade in short term, possibly a good reason not to climb to the maximum possible altitude straight away? If its that tight a margin on performance then perhaps the operator should mandate you put the transponder to TA only? Just a few thoughts, but I reckon following it as best you can would be the best bet.