Plus sized for a runner... Why does it matter?

When looking at the sizes of the elite runners, I realized I weigh a lot more than them. Even though I look like I weigh 100lbs soaking wet.. I don't. In races I've seen girls larger than me killing it and finishing faster than me. There are so many articles on losing weight with running and smaller = faster. Is being the smallest you can be really the key to success? Or, are these girls who get paid to run hundreds of miles per week just that small due to the amount of miles? I think every runner who competes even on a recreational level questions this. According to these lovely ladies stats online, I'm plus sized in the venue of competitive running.
For me this has only to do with running. If your not a complete bat shit crazy runner, who gives a shit what your size or weight it. As long as your healthy and happy... own it! Unfortunately for me who wants to be the fastest I can be, this becomes an issue. I've stayed in the same ball park weight throughout all 3 of my marathons. I'm still at the weight as I get closer to Paris. I know that my disgusting habit of smoking contributes to my turtle pace but is my weight also an issue. Of course my nutritionist and therapist say "fuck no!" but they also look at my BMI and getting me sane. They are not really concerned about my pace per mile.
They all say I'm pure muscle and I don't want to lose any muscle I've obtained but, if I was smaller would I go faster? It makes sense, the less load you have to carry 26.2 miles, the easier it will be. As anyone will tell you, it's hard to lose in training. Maybe the real key is to run more miles. I've tried everything and I actually eat a lot less than the elites do. I also have a full time job and can't run a marathon every day. Maybe it is all about training. Maybe until Nike signed my ass and I can run full time then I have to be happy with my slow progression. Either way I will do everything I can to succeed.
Only 53 days until my Parisian dream comes true. What my end result will be... 4/12/15 we shall find out. I'm still feel not completely ready but I have some time. Hopefully I'll find a great outfit and I hairstyle that will actually stay put! Hopefully I won't shit my pants and be happy with my time. Looking like an ass in Paris is not the goal!