Pentium® Processors-Quick Reference Guide http://developer.intel.com/design/pentium/qit/ has details on specific ship numbers.

SL27H
Processor CPUID Information
Type 0
Family 5
Model 4
Stepping 3
Mfg Stepping xB1
Part Number
Processor Part No. FV80503166 SL27H
Installation Information
Operating Voltage core operating voltage 2.700V - 2.900V
Bus Freq. (MHz) 66
Core Freq. (MHz) 166
Bus/Core Ratio 2/5 Ratio
Timing Specification Standard
Package Information
Pin Count 296
ZIF Socket Type Socket 7
SY059
Processor CPUID Information
Type 0
Family 5
Model 4
Stepping 4
Mfg Stepping xA3
Part Number
Processor Part No. FV80503166 SY059
Installation Information
Operating Voltage core operating voltage 2.700V - 2.900V
Bus Freq. (MHz) 66
Core Freq. (MHz) 166
Bus/Core Ratio 2/5 Ratio
Timing Specifications Standard
Package Information
Pin Count 296
ZIF Socket Type Socket 7
http://developer.intel.com/design/pentium/qit/database/SL27H.htm
This is a desktop Pentium® processor with MMX™ technology		 http://developer.intel.com/design/pentium/qit/database/SY059.htm
This is a desktop Pentium® processor with MMX™ technology

Intel Pentium® OverDrive® processors with MMX™ technology http://www.intel.com/overdrive/personal/odpmmx.htm Explains how OverDrive® chips have on-package voltage regulation - adapts 3.3v system voltage to 2.8v processor voltage