"No pressure issues that I can see and according to Speer I have another grain to go before max charge. Another thread here suggested that Sierra's suggested max load was way below where I am now..... "
There is no reason to think so. Sierra's load was developed in Sierra's lab/test rifle. Speer's was done in theirs. Yours is neither.
"Is it necessary to use the specific reloading tables for bullet brand/type?"
Not at all.
(I can hear the gasps of shock and shouts of denial already! No matter, it don't matter which book you get the data.)
In fact, what you already see in the Sierra and Speer data, added to your own experience, proves that NO pressure issues from component changes are nearly as large as the differences in the rifles they are fired in. That means you can consider ANY load data as generic, all applying as just as well to any bullet of the same weight. No book info can be more than a general suggestion, we still have to prove the results in our own rifles. (Ditto OAL)
"Start low and work up.....," etc., fixes it all.
royinidaho, above, gives you a good condensation of years of solid experience in his simple wisdom. Listen to him!