The 4100 is good, the 4300 is a turd.. it came around in '67-'68 to 'replace' the 4100 for emissions needs..
For a stock 289 I'd say a 500 would be better, the 4300 that came on stock 289/302's flowed 441cfm IIRC...
The difference between a 600 & 500 Edelbrock (or Carter) is the secondary venturi size, so the extra cfm doesn't matter until you stomp on it.. the venturis are also removeable, so you could feasibly change them later (if they sell them individually, not to sure on that one..).. Although the calibration (metering rods,jets,springs) will probably be a tad leaner for the 500 vs. the 600.
The electric choke versions are calibrated more for economy(mpg), and the manual choke versions are calibrated more for performance (richer).. according to the catalog.
I run a 600 Holley vac sec on my internally stock 302 in my '68, and it runs fine... it runs a HELL of a lot better than it did with that 4300.. all the way around, power, mileage, everything.. .I even ran a 600 cfm 4100 of my '65 Galaxie 390 for a little bit, and the Holley would kill it big time.. I've never had any 'leaks' with the Holley.. and my car has been sitting for about a year and a half, I start it up once a month, and I have had NO probs with leaks... That 4300 sure did leak tho, like a damn GM quadrajet...