Which version have you got? Their AR or RFS suffixed 70? I suppose we should be sure we're comparing apples with apples.
I understood from non-anti OS prejudiced reports here that the current model Surpass II certainly kicks the AR's arse, and is still more powerful than the RFS as well? I know from personal experience that whilst it looks impressive on paper, IMO&E the 61AR is sick when compared with an OS 52 Surpass, and the low end carburation issues OOTB simply make it not worth the trouble. The 70AR performances I've witnessed are at best described as "ordinary". We haven't seen the RFS here as they've only just started distributing them. The 70 is the only RFS capacity currently available locally, presumably wanting to exhaust remaining stocks of ARs in all other capacities prior to importing RFS's.
Longevity wise, I don't think current Magnum P&L longevity will be any more of an issue than current OS models. Oil education and run-in procedures are the problem with so many RC flyers today, so many observably lacking the acquired knowledge and basic skills derived of an apprenticeship necessarily served as aeromodellers in the hobby demanded of a bygone era. Certainly not seeing any evidence of reduced longevity due manufacturing issues this side of the pond. Only reason I can think of in terms of value not to buy a Magnum over OS at this juncture is simply their hit or miss carburation issues with some models. eg: XLS52A, FS-61AR.
On that power comparison between the RFS and Surpass II, I'd only be too happy to be wrong, and freely admit to not being interested in researching it further to establish 'the irrefutable argument' either way, as its all of merely academic interest to me at this juncture. Even the vanilla Surpasses certainly made the ARs look sick. But I digress. Suck and blow. Anything more complex is superfluous affectation.
Just a point of note, using a silicon exhaust deflector will significantly effect a reduction in power available from two strokes in vertical. They act as a choke under load. Unsure of how detrimental their effect upon mechanically timed and valved four strokes.