You need to remember that since the change to WSOp you have no guarantee of becoming a crewman, although there is a fairly good chance at the minute with the current front-line manning situation. However, if six years or more in the north of Scotland on Nimrods, with 6-7 months a year out in the desert doesn't float your boat, then I'd suggest you have a careful think about your future.
SAR helicopters are available for ALL WSOp trades and most RadOps are ex-Nimrod rearcrew. Also worth bearing in mind is that the SAR(H) transformation will start from 2012 onwards, which will massively reduce the military helicopter crew numbers. Those left in the SAR Force will alternate between SH and SAR tours which you may not find too appealing.
At 30, if you're fit and healthy, your maturity will be an advantage and will probably increase your chances of a first tour on SAR more than your mountaineering qualifications. As for you girlfriend, at 30 you'll also what's more important.
All the best with your decision.