Do you have a furling mast? If so the amount of tension must be somewhat limited to keep the mast straight enough for the furler. You can add a little tension to the lower shrouds to minimize bend while increasing backstay tension but only so much until the upper shrouds get loose anyway.
Our 37 came rigged from the dealer with the backstays pretty tight, but the uppers had a quite a bit of slack as a result. Our yard did some tuning to ease the backstays, which let more of the load go on the uppers and keep them more firm. Unfortunately after that we seemed to have more forestay sag. I added just a little more tension to the backstays and uppers and have everything a little better balanced now.
My previous thread on the subject -
Appropriate amount of headstay sag?