No. as long as it's active the speed remains the same. yes chakra amount dictates their speed, but only if it's released outward for shunshin and by that I mean the overall body (feet technically). example: the raikage always had bijuu level amount of chakra but he had to expel/release it outward to access his new mode to accomplish a higher speed but as long as he's in that mode his speed remains the same no matter what. same w/ naruto bm. I've read this whole manga and never ever seen a character dip in speed in the same mode, not gaara. not kimimaro and not 5Glee. kaguya did but she's literally the only character who doesn't use shinobi techniques and oddly her strength of attacks decrease over the course of the battle due to overusing her chakra. that doesn't happen to ninjas, when they get tired either 1. they drop to a weaker mode. or 2. not be able to use that said technique at all. there is no such thing as accelerate/deccelerate speeds from the same chakra source that was sustained
Obito himself is actually very strong lol please, he was about the same level as kakashi in H2H combat.
naruto was pretty low on his own base chakra. lol has nothing to do with his speed when in kurama mode, man. don't think naruto officially runs low of chakra in base and kurama chakra until later in the manga when neji died which takes place far after the madara and obito examples I've gave.
Raikage had a special technique called the lightning cloak which was using lightning nature to increase his normal top speed. His lightning cloak doesnt burn through chakra to stay active though.
Bm combines narutos chakra and kuramas chakra into one. The more chakra used, the slower they get. Especially since it burns chakra just to stay in the mode.
I mean its hard to explain. Look, in BM, naruto only needed to use a certain amount of chakra to keep up with people who were much slower than him, so it appeared that naruto never got slower. Like, if BM naruto fought base kid sasuke, it would take very little of BM narutos chakra to outspeed sasuke, so BM naruto would be able to keep up the same speed that would outspeed sasuke for a long time. It depends who BM naruto faces, as well as how much chakra BM naruto has at the time he faces them. Usually when naruto faced ppl in BM, kurama had all his chakra, but naruto didnt. Naruto ran low on his own base chakra a few times throughout the war.
War arc kakashi wasnt weak at all, so lets get that out of the way. Although when he fought obito, he was very injured, tired, and didnt have much chakra compared to his full reserves, due to all the fighting he just did in the war. And you do know obito was holding back against kakashi, right? It was literally stated that he was. You can find it, you should already know this anyways.