Chad all companies I have ever interviewed, especially those rep'ed by headhunters, claimed "year end bonuses averaging around 10%". Even my current company which I have been with 3 years claimed such and I have never received a bonus from them.
If you get to the point of an offer, request a signing bonus and state the rational for the need is that your current company offers YE bonues too that are paid in March (assuming this is true) and you would be foregoing that should you leave now. If they are unwilling, then their bonus policy probably isn't that "secure", because these things tend to come out in the wash (e.g. they should also have someone who is leaving or left in December if they are a company of any size, and you would be getting his/her portion from the bonus pool).
Furthermore, regarding benefits, "times change", and the company that is doing well now might cut costs and bonuses by YE next year. The only things you can count on are salary and vacation time. Medical insurance contributions tend to fluctuate too so you can't count on them. Headhunters always paint a rosey picture.
If you consider this job and begin to negotiate, try to maximize your salary AND your PTO (paid time off) and don't fall for the "it's our company policy" line with regards to time off allowed. People move around moreso these days, and having to reset your vacation levels to 2 weeks (or even lower) just because you take a new job with a new company, especially if a seasoned professional, is unacceptable and not competitive.
Good luck.
TJR