1. => Used with LO > 8MHz and 100kHz devices
Yes.

2. => Time Delay during acknowledge?
Not Exactly, data transfer can be paused by the receiving device by holding the clock line low, so the receiving device can control the data flow. To enable this function you need the DEFINE I2C_HOLD 1 declared.

3. => Open Collector / Bipolar Clock on SCL? Dont Understand this!
Joe already answer to this point with a clear explanation. Let me add that bipolar is a device capable to pullup the lines by itself without the need of external pullup resistors

So: I use PCF8575C and MAX3611 (both 400kHz devices) but both only work
correct when DEFINE I2C_HOLD 1 and DEFINE I2C_SCLOUT 1 is done.
It is usefull to use DEFINE I2C_HOLD 1 as default since it will keep synchronized different devices connected on the I2C bus all with different internal clock.

I don't know much about PCF8575C and MAX3611 but very likely they are bipolar devices.

Al.