Turned out I needed to change not just the X and Y maximum accelerations but ALSO the one labeled "Acceleration" and "Retract Acceleration".  Still got some dialing in to do but it's now off by a few minutes in a 10-minute print vs factors of 3-4x longer.

Also I did discover you can change the settings just thru that EEPROM GUI and they seem to stick, no need to re-flash the firmware.  In fact, you can apply the changes DURING a print which will make tweaking a lot easier.

I've attached a screenshot of what I'm currently using, I had it up a fair bit higher at one point and it was running amazingly well but the printer started smacking the wall because the whole wire shelf my computers/printer sit on started to resonate dancing several inches back and forth.

At least I now know what I'm dealing with and how to tweak it, thank you very much for the help!

It won't exceed the max accel set in the firmware.  Set x and y at 2000 anyplace you see the 1200 value for those 2 axis.

Ah, ok.  After I finish this long print I'll give that a shot.

Right in the configuration.h file but they should be already set at 2000.  You can also take a look at your Max Speed settings

That'd be the "DEFAULT_MAX_ACCELERATION" line?

#define DEFAULT_AXIS_STEPS_PER_UNIT   {88,88,2268,138}  // default steps per unit for Ultimaker {SD Patch}
//#define AXIS_STEPS_NEGATIVE           {88,88,2268,138} // Step values to be used when travelling in the negative direction. Useful for threadless ball screws. Comment out if not needed
#define DEFAULT_MAX_FEEDRATE          {500, 500, 5, 45}    // (mm/sec) {SD Patch}
#define DEFAULT_MAX_ACCELERATION      {1200,1200,100,10000}    // X, Y, Z, E maximum start speed for accelerated moves. E default values are good for skeinforge 40+, for older versions raise them a lot. {SD Patch}

#define DEFAULT_ACCELERATION          1000    // X, Y, Z and E max acceleration in mm/s^2 for printing moves {SD Patch}
#define DEFAULT_RETRACT_ACCELERATION  1000   // X, Y, Z and E max acceleration in mm/s^2 for retracts {SD Patch}

Attached is a screenshot of what it shows in the settings menu of Repetier Host, I'd used a "M201 X9000 Y9000 Z100 E10000" command to test changing the max acceleration based on some other forum info but it doesn't appear to make a significant difference.

Does it only use the hard-coded settings?

Increase your acceleration speeds to 2000.  This will get your printer shaking again and bring those estimated times closer to reality.  I don't know what firmware you used but for that machine you want https://github.com/ozadr1an/Solidoodle- … n_v1_beta.

I believe that's the one I downloaded.

Solidoodle-Marlin_v1-Solidoodle_Marlin_v1_beta.zip

Is that just acceleration speed in the printer EEPROM settings or someplace else?

A few months ago I attempted a firmware update on my Solidoodle 2 to allow for PID control on the heatbed.  I ran into a few issues and ended up having to recover by using an Arduino ISP to reflash the printer's firmware.  Also I had to change a couple lines to make it work right (like add the line at the start of the main which tells Repetier that it has adjustable speed).

About the same time I updated Slic3r because a few parts failing to slice and the update appeared to fix that, unsure if this could be related or not.

When I finished it'd done some quick test prints and it seemed to work fine but now I've noticed that on larger parts the estimated time is WAY off.  It used to be "fairly accurate" within say 15 minutes on a 8 hour print back when the printer was totally stock but now it's about a factor of 3-4x error in the estimated print time to the actual time.  Yesterday afternoon about 3PM I started a 12-hour print and at 200% speed it didn't finish until this morning around 7AM. even though the estimated time at 200% was only 6 hours.

I've also noticed my printer doesn't "jump around" as much, I recall the whole machine used to nearly shake itself off my stand at 200% speed and now the frame just quivers a bit.

Can anyone give me any suggestions where to look?