[reSIProcate] reSIProcate vs sipXtapi

[Diego Susa]

Hi:
I'm new to SIPFoundry's set of tools, and I'm actually facing a kind of "dilemma".

As far as I understand, reSIProcate is a SIP stack library. On top of reSIProcate sits DUM, which is an application layer library that makes reSIProcate easier to use (a kind of framework I guess, because it's callback programming style makes heavy use of the IoC principle). I think the key-point about DUM is that SIP communications can be programmed in terms of the "Dialog" abstraction, instead of dealing whith the "raw" SIP messages.

On the other hand I've found sipXtapi, based on sipXport/sipXtack/sipXcall/sipXmedia. It seems to me this is "another" SIP stack library (with a different code base) than reSIProcate... am I wrong ?
In this case I think the "stack" portion is sipXport/sipXtack and the "simplified" use of this stack comes in through the "TAPI" (traditional telephony) abstraction: sipXcall/sipXtapi.

The main question is: why there are 2 different SIP stack implementations in the same organization ? (I guess there might be some trade offs between historical & technical reasons, ...but which ones?)

Then the very final question... 
If I had to build a B2BUA as quick as possible (like every project in this telco world), should I choose "reSIProcate + DUM" or sipXtapi ??? 
which would be the advantages and disadvantages on each side ???

Having a first bird-eye view: I believe sipXtapi would be the "easiest way" (having a telephony background, as is my case); but it also would be the worst about scalability (because of the media handling). On the other hand "reSiprocate + DUM" seems to be the best choice about scalability, but is harder to start with (I haven't found a single example of true B2BUA functionality; and the svn examples are not enough to make a test with the simplest scenario: "Flow VI" of RFC3725 ... URLs/tips regarding this would be of great help).
Could anyone point another advantages/drawbacks of each choice ?

Thanks in advance,
receive best regards...
Diego

PD: I'm posting this to both sipX and reSIProcate developers because I need to hear both kind of opinions. Assuming they're not the same group of people, there could be some different "points of view" on each side :-)