It is right you gain best in 40-60% success range. But - a general rule, is as long you can fail you can gain. My experience with training taming, is stick to where you can fail. When the fail rate is too low, I jump higher.
I have completed quite a lot of tamers up till 110 taming, and - it is doable to go 50-110 taming in 5 days. For that, - I had only taming and lore on the toon and minimum of magery. I did no jewelry boost, hittet polars and white wolf's till around 90. Then Bulls till I hit 105 and ki-rin's from there in ki-rin passage...with a 2nd acc helping to drag off the paragons.
If you boost your taming with jewlry, you only go to a higher critter that is more difficult to tame. It is no sence in that - as it will not benefit you. You will gain what so ever according to your success rate - not more often cuz it is a higher creature. The critters cover its all for you to avoid doing that and gain on easier pets. For bulls, you can gain untill you are 116. I did my last tamer on bulls till 110, no hazzle - and the gain frame is about the same as with ki-rins.
Besides, training other skills - the chance of gain the lower your skill are is higher. Take magery...equip -29 mage wand and you gain instantly all the way till 60's.. drop wand go get discoed, and equip it again...and you continue gain in same speed - take you all to 80's in a hr.. That you can not do with normal training.
The gains are based on your modified skill, and how high it is...the higher - the harder.