I know this topic is brought up alot and there are many, many outlining issues that may effect results.
(Too many to begin to even list actually)

...................But here are my results from a 1992 Progressive, where I ran into a bit of an issue at ss/2b. All my own fault.

Against RHP, I have been playing a 1b at 2b and a 2b at ss.

2b Ryne Sandberg, (A.A-, .990, 5.67rf) No other defensive ratings. He's my ss @rhp.
1b Cecil Fielder, (C,C, .991, 9.55rf) No other defensive ratings. Yup.......he's my 2b @rhp.

Both shift to their natural positions @lhp.

Sandberg's line:

Pos	GP	GS	Inn	E	Throwing E	PO	A	DP	Good Plays	Poor Plays	F. Pct	SB	CS	C. ERA	PB	PK
2B	40	40	358.3	1	0	101	102	20	4	0	.995	0	0	0.00	0	0
SS	65	65	567.3	11	0	140	211	46	1	1	.970	0	0	0.00	0	0

RF's 2b 5.1 ss 5.57

Fielder's line:

Pos	GP	GS	Inn	E	Throwing E	PO	A	DP	Good Plays	Poor Plays	F. Pct	SB	CS	C. ERA	PB	PK
1B	36	36	315.3	0	0	321	24	22	0	2	1.000	0	0	0.00	0	0
2B	65	65	532.0	20	6	140	166	36	0	4	.939	0	0	0.00	0	0
LF	4	4	34.0	0	0	4	0	0	0	0	1.000	0	0	0.00	0	0

RF's 1b 9.85 2b 5.18 LF 1.06

I have Gallego, Trammell and Arias in a ss rotation @lhp. (@335pa total)
I felt that Sandberg's A,A- was a better potion than trying to rotate the other 3. And so far, he hasn't been a problem at ss.

League is 105 games in.

Not bad. I'm surprised Cecil hasn't been worse. 

Yeah, I would have expected Cecil to be a Ceaser Tovar level of bad....something like .850 fielding % and a "-" play every 18 innings or so.

Fielder's RF is GREATER than Sandberg's and seems to turn more DP's.   Odd....

The team has actually turned the 3rd most DP's in the league(227)? Range 232 - 153

Sandberg's line was pretty much what I expected, but Fielder's is a strange bonus. 20E and only4- plays in 65 starts is not average, but for a team in the lurch, not a bad tradeoff for .273 and 19hr.
When I saw his RF, I had to refresh the page to make sure it wasn't a browser issue. I understand there are a myriad of calculations involved in this game, not caring to understand them at all though. Fielder's RL rf of 9.55 does not seem to be out of the norm for 1bmen?

Like many progressive owners, I sometimes play players OOP from time to time to fill needs. I misread/forgot Trammell's 93 was only @115pa's. A real WTF moment.

In playing players OOP, I have found 1bmen play solid in LF also.
One thing I firmly believe is that the majority of the time it is far better to play a player w/o a rating at a position, then to trot out a D-D-.

As an addendum at 1b, as you probably guessed, I have another platoon. After 112g:

@rhp Brett RL#'s       DD .990/8.87  Simstats:  79g 74st 660in  687po 75as 4E 2-  .995/10.40
@lhp Fielder RL#'s   CC .991/9.55  Simstats:  38g 38st 334in  344po 27as 0E 2-  1.000/10.02

I would have thought a DD would not have performed as well?
Taken in our aaa phase, Brett's hitting .339 31 2B in 340pa's.

I know  a defensive 1b is not AS important in the spectrum, but from experience a D-D- 1bman has performed very bad. (higher (-) plays, a few more errors and a RF south of 10. Brett has defensively exceeded expectations as well as Fielder(2b).