I have a 6" spike running around that looks to be 2.5 at least. What do you look for to decide he has to go?

Shoot all spikes! Less than 50% of spikes ever attain 8pts or more while almost all deer with 6pts or more as yearlings attain eight pts or more. It's rolling the dice, most of the time when you try to cull any deer, but a spike is always your least likely produce in the future. TPWD says that one the worst run range in the worst possible year for growing antlers there will still be yearlings with forked antlers, therefore even a deer who is a spike because of bad conditions that year was probably inferior to other deer at growing antlers. When you shoot a deer with fewer than four points you can be certain that you killed a deer that did not have the best genes on the property. When you pass a spike you take a chance that you let a deer walk , that might have had the worst genes on the property, or might be decent, but you know he doesn't have the best genes.

Just what you described. Long spikes and 2.5=

One horn on each side and he needs to go. Just my honest humble opinion.

TPW has a document on their website that suggests shooting all spikes at 1 1/2 yo or older.

The problem with all of the so called "SPIKE" studies, that I have read about,don't differentiate between spikes born on time vs. spikes born late to fawn does. My opinion for what it's worth, is as stated above. If it is 2 1/2 years old and a spike, "KILL HIM", he has had plenty of time.If he is a small(the size of a doe or less) 1 1/2 year old,then give him a chance.Again-JMO