hehe~~~watch some episodes of "sex and the city" and try getting somet answers there. :p
But to me, it doesn't matter. Don't be bothered by the difference of two simple phrases. Lovers do whatever it leads to, either fast or slow. If you have particular requirements, say it out. Otherwise, he wouldn't know.
个人感觉楼主理解得挺正确,having sex 重点是sex,主要是生理上的满足,making love则有感情成分在里面。比如和一个陌生人的one night stand, 通常不会用making love,而会用having sex,和你相爱的人,则通常会用making love。搬一句网上看来的定义: making love is having sex with the one you love.