[j-nsp] MX104 capabilities question

[Ralph E. Whitmore, III]

I am in the process of replacing my old cisco650x hardware and was steered to this list to pose the following questions:

I have 4 primary BGP transits  each delivering 600k+ routes to me and we will be adding another probably 600k+peer in the near future.  The sales rep recommended the MX 104 to us first, but then came back to us and said "Sorry this router isn't adequate for your needs you need to be in the MX240 Chassis" I read the spec's I can find and it says from a routing engine perspective (RE-S-MX104)  that it will handle the routes with room to grow on."

>From Juniper:
IPv4 unicast FIB 1 million
IPv6 unicast FIB  512K

Ipv4 RIB   4 million
IPv6 RIB  3 million


So the question is:  is there some other limiting factor(s)  that should steer me away from the MX104 to the MX240 Chassis? Is the sales rep blowing smoke?  I am hoping to find someone here who has tried this config and will either say yes this is great solution or  OMG, I'd never try that again.

Thanks

Ralph