I am currently shooting a 2002ish hoyt magnatec with a 28.5"draw.I chronoed the bow tonight at 261fps with a 400 gr arrow.I am considering  a Obsession def con 6, that will push that same weight arrow at around  317 fps with that draw length.
My bow is not only slower, but it is pretty loud, and the lack of let off is a shoulder killer.
Now, my bow has killed every deer I have every shot at with it, so I can't really decide  if it would be worth the $1300-1500 for a new bow.Any input?

That's really up to you, no doubt the newer bows are faster but as you stated what you have will certainly kill deer. Yeah, the new one will shoot flatter, the 3D guys like that especially at the longer stakes as it helps with small errors in range estimation. If you are  comfortable with your current setup, range find your area then speed would not really be that big an issue. The one thing you said that would be a bigger deal to me was the noise. I'll leave it to you on how big an issue the let off is; some guys say the more the better, others like a bit of holding weight. My bows have zero let off so my opinion is pretty useless there!

What kinda of broadheads do you shoot?  Faster bows are harder for me to tune to fixed blade heads.

Muzzy 125, fixed blade.

you may experience the same trouble I have now, fixed blades like the muzzy at 300+ fps will have a near impossible time getting to shoot like your field point.

In a tuning class put on by the local guru, he confirmed what I have been pulling my hair out over... you can get close, but not dead on.

On the new bow subject... if you can afford it, I'd say go for it, faster and quitter are nice 14yrs out of a bow aint bad, keep it as a back up or sell it to pay for a new sight/rest

Agree with the fixed blade tuning issues. My last bow I got 5-6 years ago started that for me. I then switched to mechanicals with no issues though. They fly like my field points and have done the same damage.

If you're killing them and holding it back just fine without a need for more let off and happy keep it. If you want to try something new just shoot a new bow at your dealer. Maybe that'll make up your mind!

My bows are both 2012 models and I want a new one, so I'm not a good measure of when to replace it.

As for the tuning issue, it can be a matter of "preference" for both your bow and your shafts. I found this out with the crossbow and it makes more sense to me - any sort of "standard" broadhead did not fly well compared to field points or bullet points. While relatively consistent (accurate enough for deer), they just didn't fly the same. Field points and bullet points would pile up in the target, while broadheads would be 2-3 inches below (always) and somewhat off on windage. When I switched to CX XT dual blade serrated, I found that they flew exactly like my target points. It's a short broadhead, and that seems to make all the difference - using a 2+ inch long broadhead on a 20 inch bolt adds enough to the overall length and FOC that you can alter the accuracy. While my compounds are less sensitive to this, it is true that the "crossbow" broadheads fly a lot truer. Something to consider.