[quote=@Kho]
Will get a post up soonish. Great to be part of this, really hope it becomes something ;)

What are everyone's thoughts? Would the Muslims have reached their levels of success if Rome still existed in east and west?
[/quote]

A Rome that holds the West that just means more borders to defend. The 30 year war against the Persians probably exhausted the Empire (or at least the Eastern portions) as much as it did IOTL, but unlike the Byzantines IOTL Rome has much more territory to defend. It's very plausible that while Rome was focused in fighting off the Sassanians, the Franks/Vandals/Visigoths and etc seized the opportunity to increase the pressure on the Western half of the Empire. Which would pretty much negate the advantage provided by having access to more lands and manpower. Of course, down the road a larger Rome might be able to muster enough strength to check the Islamic advance somewhere along OTL lines (maybe hold on to bits of Africa). But even then they would always have to be on the lookout for their other neighbors looking to profit on the weakness of Rome.

Taking the IC situation as an example we have: A Roman army, led by the Emperor's third son, crushed by the Caliphate. Sure, Emperor Marcellus could in theory muster another army and march East to stop the Muslim advance and restore the status quo. But if he were to do that the western half of the Empire would be left vulnerable. After all the reason why Priscus was sent to Syria is because Marcellus is busy fighting the Lombards. So from my point of view the situation in the Roman East isn't good, they have the power to beat back the Arabs but they have too many enemies to focus their effort on just one of them. And until they can do so (maybe if Marcellus defeats the Lombards decisively) the Muslims will have much more freedom in the Roman East.